600yard 223rem loads

I'm looking for a load that will be accurate enough to hit a shillout at 600yards
my rifle is a mossberg map varminter, 24inch barrel, 1:9 rifling, uses ar mags, right now I've been using 53gr vmax and 53gr tsx, i was looking toward the 75gr amax but was told i can't fit the round in an ar mag, so what you guys recommend, powder recommend, bullets? Cases? Primers? Tricks for preping the brass?

75 gr AMAX won't fit in magazine. 75 and 77gr hp will nicely. Some 1-9 twist will stabilize 75gr hp. 24" barrel will help. Need to try them. 24gr Varget or Reloder 15 or TAC should work. Work up to this however.

I'd have to look at exactly how much Varget I was using Sierra or Nosler 77gr BTHP's seated about .01 off the end of the magazine (I don't have the actual length handy at the moment). Never had a problem, and suckers shot great.

While I'd agree that a 75gr A-Max won't usually fit in an AR magazine, I shoot A-Maxs loaded long and single load them with Varget .010 " shy of the lands.
Personally, I haven't had any luck shooting 75s in a 1/9 barrel but you may be blessed?
In your situation, I'd try 69s, long and hope for no wind condition.

You will just have to try the heavier bullets and see if they keyhole. It is not a hard limit but most 1:9 barrels won't shoot anything heavier than a 69 SMK. A bud of mine shot 75 AMAX in his 1:9 and it worked out to 600 yards. I have seen others try heavier bullets in their 1:9's and not hit the bull at 300 yards.

I have shot the 69 SMK at 600 yards and it is wonderfully accurate. But the slightest puff of wind and that bullet sails off to the side.

Personally, I haven't had any luck shooting 75s in a 1/9 barrel but you may be blessed?

Click to expand...

Which 75gn? Hornady makes two. The Amax will not stabilize in a 1:9 the BTHP is a great deal shorter and usually will. The Berger 70gn VLD should also shoot well from a 1:9 barrel. It has a higher BC than the 69gn SMK and the Hornady 75gn HPBT. Its not quite as high as the Amax but that's the price you pay for being able to load from the magazine and stabilize in a 1:9 barrel.

The 53 grain Vmax is my load of choice out to the limit of my range, which is 550 yards. A 1:9 twist should be a perfect match for the 53.

If you look at the ballistics of that bullet you'll see that it gives up very little to any of previously mentioned bullets, and outperforms them all at shorter distances and costs a whole lot less.

Once you get past 600 yards then the 53 Vmax starts losing big, but if you're only shooting out to 600 yards, then you may just be spending extra money on bullets you don't really need. The only other question is whether your rifle will shoot the 53 Vmax accurately.

The Sierra 69gr MatchKing bullet Part #1380 should work very well with Varget for what you are looking to do. You might also give the Hornady 68gr BTHP bullet Part #2278 a try bit I can't comment on it's accuracy because I have not tried them yet. I have shot the Sierra bullets.

kingcheese
I have good luck with my 223, 24" Heavy BBL 1:9 twist using 53grn A-Max, 60grn V-Max and 69grn Nosler CC with Varget and TAC. out to further ranges. Wind drift becomes a real issue however at the longer ranges.
Bullets are set .020 off the rifling and will not fit in the magazine, shooting single shot hand fed.

- could never get the same degree of elevation control with the .223 that we could with the .308

- the theoretical wind drift advantage of the .233 just didn't amount to anything worthwhile in real shooting, especially in light of the increased elevation dispersion.

The .223's small case capacity and powder charge, however, are the root of another significant and perhaps insurmountable problem causing elevation dispersion - the primer ... primers just aren't as consistent as we want them to be. Their method of manufacture almost guarantees a significant level of variance in their power output.

The lowest standard deviation (SD) of chamber pressure was 400 psi with a corresponding extreme spread (ES) of pressure of 1,400 psi. The largest SD of pressure was 1,400 psi with a corresponding ES of pressure of 4,100 psi. These were all high quality primers in use by Highpower competitors, not bargain basement off-brand stuff.

... The .223 case has less metal surrounding the primer pocket than any other case used in Highpower shooting; add in the typical .223 shooter's propensity for heavy loads and you get the blown primer pocket failures that we see every week with this cartridge. Going back to your earlier comment about the increased effect of charge variance on pressure in the .223, consider also that the smaller case responds more dramatically to changes in temperature (and absorbs chamber heat more quickly); it's really just a recipe for disaster.

... point is that if the .308 isn't exactly ideal, the .223 is far worse. Everything that limits the .308 can be said with even greater emphasis with respect to the .223.

I would think anything longer then a 65gr Serria would have FITS trying to stabilize in a 1:9 twist, a 1:9 is best suited to the 55gr class stuff, you can still shoot 600yd with it but on windy days you will wish you had a 1:7" slinging 80gr VLDs or 77gr SMKs. Better yet a 308 or 6.5x55

The 77 grain Sierra Matchkings are designed to shoot well when seated to magazine length. It's all in the design of the bullet ogive and Sierra made these specifically so Highpower shooters could shoot a heavier bullet from a magazine during the rapid-fire stages. How well they will shoot out of your 1/9 twist barrel is debatable but of course there is only one way to find out. I've shot tons of these bullets (from a magazine) out of my 20 inch 1/7 twist AR for highpower competitions at the 300 yard line and they shoot exceptionally well for me with 24 grains of Reloader-15. This is a slightly compressed load. If your twist rate is enough to stabilize them they are definitely capable of hitting a silhouette at 600 yards. I shoot the 80 grain Sierras at the 600 yard line because of the sleeker, higher ballistic coefficient of the secant-ogive shape, but they aren't designed to be seated at magazine length and must be loaded single shot.

I got keyholes at a quarter mile with 77gr sierra Matchkings, ended up building a different dedicated upper with a 1:7 twist barrel in 223 wylde, which worked out real good. The only downside is that particular barrel don't shoot 55 gr for jack, and 60 grain is not great. The 223 Wylde has a heck of a long throat before the lands, meant to load bullets overlong and single feed. 55-60gr loaded at magazine length they jump so far to the lands they get a lot of velocity spread, and some runout.

My High Power shooting buddies tell me you just have to try different bullets to see if the 1 in 9 will stabilize them. I set up a 600 yd. range here at the house for the Jr. High Power shooters to practice on before the annual trek to Camp Perry. They all shoot 75 gr. Hornady's, but I can't say with certainty what twist each of their rifles has. Remember: whether or not a bullet will stabilize with a given twist is more dependent on the length of the bullet than the weight of it.

I wanted to try to build the "most accurate AR-15 I could build." I won't lie, that upper cost me a mint to put together. And it mostly just sits on a shelf collecting dust!

The last experimenting I did on it was with seating depth of 77 grain SMK's. I've had a working theory for a while that bullets with the base seated deep in to the casing, with the bearing surface "floating in space", get perturbed and distorted prior to fully entering the throat. I first noticed the phenomenon on 300 win mag, 220 grain bullets, seated with the bearing surface deep in to the cartridge (3.300 OAL). I lost an entire MOA of accuracy if the bullet's bearing surface was seeted deeper than the neck, vs. an OAL matching my lands with the base NOT extending in to the cartridge!

The same thing happened when I tested it with 223. Seating a 77 grain bullet deep in to the case, so it fits in a magazine, shoots much less accurately than the same bullet seated over-long, with the start of the boattail matching the end of the neck. My group sizes at 1/4 mile (440 yards) were averaging about 3" with the rounds loaded long, and single loaded, versus an average of 6.5" groups from rounds seated deep and fed from the magazine. The groups opened up in each direction, but also grew oblong vertically, and the chronograph showed much a higher velocity spread on rounds seated "deep."

My theory for this is the that A] the bullet has enough bearing surface for the charge to cause it to "tilt" prior to fully entering the throat, and B] the base of the bullet actually expands under the high pressure, and then re-forms to bore diameter as it enters the throat. (Copper & lead are pretty malleable, and deform much like a wad of jello when faced with 55k PSI of pressure... The rear of the bullet is getting shoved in to a front that is facing resistance, causing the back of the bullet to balloon out slightly, then re-form to bore diameter as it enters the throat.)

Granted, I don't have the ability to SEE this happening, and can only form hypothesis based on external data gathered, but the velocity spread difference was pretty telling!

I ALSO believe that the 1:9 twist issue on 77 grain that SOME people (including myself) have seen, with bullets not stabilizing, while OTHER people can shoot those just fine out of the same twist barrel, has a LOT to do with where the leads are located and how much throat erosion there is.

If the bullet has sufficient free-bore (from an eroded throat) it will "skip" ahead in the bore much easier, the base won't expand as much under pressure, and the bullet will be a little less likely to tilt under pressure as it engages the lands.

The only data I have to support that theory is from shooting 77gr loaded to magazine depth out of a 16" barrel 1:9 twist that keyholed at 440 yards. The barrel was brand new, the lands were sharp, and the measured velocity spread was MUCH greater than from my experimental 223 wylde chamber which has an additional .25" of freebore over the standard AR barrel (by design, for seating 80 gr bullets overlong).

The same load in one rifle was engaging the lands almost immediately, while the base was still very deep in the cartridge, while on the other rifle it skipped forward without resistance .25" allowing the base to almost clear the cartridge before engaging the lands. The velocity and accuracy was still not close to what I got with the bullet loaded long, the freebore pays a price...if you don't take advantage of it.

So my theory on that is the 1:9 twist barrel CAN stabilize a 77 gr bullet *IF* the lands are somewhat worn. (There might also be a chrome lined barrel vs. steel difference, too, but I haven't tested the differences as I don't have a non-lined steel barrel handy that's 1:9, only CM.)

Anyway, that's the whole story on the "experiment."

I have 12 different AR barrels sitting on a shelf downstairs, various gas length, various designs, various profiles, various muzzle breaks, it's fun to experiment if your willing to take the time with a barrel wrench.

Its a pretty solid rifle, the at mags give me the ability to hold as much ammo as i need, i can load it with the with the bolt closed, mags are fairly cheap, i had mags, my friends use ars so in a practical situation itmeans that i can use their mags, the action is smooth the ability is there why would you make a rifle chambered in 5.56 use anything but the most common magazine in the world, and for further clarification, this is by no stretch of anyone's imaginations a modified ar15

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